Apparatus and method for lighter-than-air aircraft

ABSTRACT

An apparatus and associated method for launching and recovering a lighter-than-air aircraft are provided. The aircraft includes an envelope that is substantially filled before launch with a lift gas and a second gas. The lift gas and second gas are substantially separated in the envelope by a boundary layer of mixed gas, formed by the lift and second gases. The aircraft is supported by one or more masts as the lift gas is injected to achieve the required buoyancy for launch. The aircraft is then released and rises, for example, in an inclined orientation. As the aircraft climbs, the lift gas expands in the envelope, and the second gas is vented therefrom. During horizontal descent, air can be pumped into the envelope to maintain the envelope in a substantially filled configuration. The air and lift gas can be mixed to avoid sloshing and pooling.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to lighter-than-air aircraft and, moreparticularly, relates to an apparatus and method for launching alighter-than-air aircraft having an envelope that can be substantiallyfull during launch.

2. Description of Related Art

Lighter-than-air (LTA) aircraft, such as zeppelins, dirigibles, blimps,and balloons typically include an envelope or container that receives agas that is lighter than air so that the aircraft is made buoyant. Thebuoyancy provided by the gas can be used to lift the vehicle to flyingaltitudes of 50,000 feet or higher, as is known for so called highaltitude platforms (HAPs). For example, a conventional blimp includes alarge envelope formed of non-rigid material that is inflated withhelium. The helium provides sufficient buoyancy to lift the blimp to itsflying altitude. Propulsion units and control devices such as fins,vanes, and the like provide power and control for adjusting the flightpath and attitude of the blimp.

A conventional LTA aircraft is typically moored to a tall mast when notin flight. A nose cone, which is attached to the nose or bow of theaircraft by battens, provides a reinforced structure for connecting tothe mast. The nose cone is rotatably connected to the mast so that theaircraft rotates freely around the mast under the force of the wind. Thefinal assembly of the aircraft can be completed with the aircraft mooredon the mast and the aircraft subsequently can be launched from andlanded on the mast. During launching, the gas in the envelope and/orballast on the aircraft can be adjusted so that the aircraft is slightlyaerostatically heavy, i.e., non-buoyant. The aircraft is thendisconnected from the mast, and maneuvering engines are used to propelthe aircraft away from the mast. During landing, the aircraft ismaneuvered back to the mast, and handling lines attached to the nose ofthe aircraft are dropped to a ground crew, which uses the lines to guidethe aircraft to the mast so that the nose cone can be reattachedthereto. Once moored, the aircraft can be refueled and severalmaintenance procedures can be conducted without bringing the aircraftinto a hangar.

The conventional mooring operation is labor intensive and expensive. Alarge area must be provided around the mast for the movement of theaircraft. In addition, the design of the aircraft is influenced by themooring operations. For example, the weight of the nose cone, battens,maneuvering engines, handling lines, and other equipment for near-groundoperation, such as ground impact protection, increases the weight of theaircraft, and, hence, the necessary size and capacity of the gas-filledenvelope. This equipment is typically used only during near-groundoperations and is unused during the rest of the flight of the aircraft.Further, the configuration and materials of the envelope and the rest ofthe aircraft must be designed to accommodate the functions and stressesassociated with the mooring operation.

LTA aircraft such as HAPs can also include a ballonet, i.e., aninflatable bladder, that is positioned within the envelope andconfigured to be expanded to nearly fill the envelope. The ballonet canbe filled with air, and the space within the envelope that is outsidethe ballonet is filled with helium. As the aircraft ascends, the heliumexpands and the air is vented from the ballonet so that the size of theballonet becomes increasingly smaller while the envelope remains at asubstantially constant volume. As a result of the constant volume of theenvelope, the aerodynamic and structural aspects of the airship remainmostly constant during flight. Depending on the position of theballonet, the center of buoyancy of the aircraft can be adjusted duringascent so that the pitch or orientation of the aircraft changes.However, the ballonet adds weight to the aircraft. Additionally, theballonet can slosh, or move unpredictably, in the envelope, affectingthe structural integrity of the envelope and the orientation of theaircraft.

According to another method for launching a LTA aircraft, the envelopeis only partially filled with helium so that the envelope is in a slackor limp condition. As the aircraft rises, the helium expands to fill theenvelope. Advantageously, there is no need for a ballonet. Further, theaircraft can be launched from the ground without the use of a mast,similar to the launching of a weather balloon, thus simplifying theground equipment necessary for launch. The weight of the aircraft can bereduced by including no maneuvering engines, nose cone, and the like.However, because the envelope is inflated only upon ascent, equipmentthat is connected to the envelope and positioned by the inflation of theenvelope may not be properly positioned and adjustment in flight may bedifficult or impossible. Some equipment, such as solar cells connectedto the outside of the envelope, can be easily damaged when the envelopechanges shape. Also, stresses on the envelope during the ascension whilethe envelope is only partially expanded are difficult to predict, andthe envelope may be damaged during ascent due to flutter or aeroelasticeffects, especially as the aircraft rises through winds, such as thoseassociated with jet streams. Since the material that is used to form theenvelope is typically only slightly flexible, wrinkling can damage thefibers and/or coatings of the envelope, causing pinholes, tears,weakened areas, and the like.

Thus, there exists a need for an improved apparatus and method forlaunching and recovering a LTA aircraft. Preferably, a large area shouldnot be required for launching, and the method should minimize therequired heavy equipment on the aircraft for near ground operation, suchas nose cones, handling lines, maneuvering engines, and the like.Further, an aircraft launched according to the improved method shouldmaintain a substantially constant shape during launch to minimizestructural and aerodynamic changes.

BRIEF SUMMARY OF THE INVENTION

The present invention provides an apparatus and associated method forlaunching and recovering a LTA aircraft in which the envelope of theaircraft is substantially filled before launch with a lift gas and asecond gas, such as helium and air. The lift gas and second gas are keptsubstantially separate in the envelope with a mixed gas that forms aboundary layer that includes the lift and second gases, therebetween.The aircraft is supported by one or more masts as the lift gas isinjected to achieve the required buoyancy for launch. The aircraft isthen released and rises, for example, in an inclined orientation. As theaircraft rises, the lift gas expands in the envelope, and the second gasis vented therefrom.

According to a method of one embodiment of the present invention, atleast one mast is provided for supporting the aircraft. The aircraft issecured to the masts while the envelope is at least partially filledwith the second gas, for example, so that a longitudinal axis of theaircraft is substantially horizontal between two masts. The aircraft canbe moved to a launch position by rollably moving the masts. A first endof the aircraft is then raised to an elevation higher than a seconddistal end of the aircraft so that a longitudinal axis of the aircraft,which extends between the first and second ends, is inclined at an anglerelative to horizontal. For example, a buoyant balloon can be connectedto the first end of the aircraft or a buoyant gas bag can be provided inthe envelope to lift the first end. Alternatively, the envelope can beat least partially filled with the lift gas and then the first end ofthe aircraft can be released so that the lift gas raises the first endof the aircraft. The lift gas can be injected through a tubular channelthat extends into the envelope and proximate an upper portion of theenvelope so that mixing of the gases in the envelope is minimized.According to one aspect of the invention, the aircraft is released witha center of buoyancy between the center of gravity of the aircraft and afirst longitudinal end of the aircraft so that the first end of theaircraft is oriented above a second distal end of the aircraft while theaircraft ascends. For example, the axis of the envelope can be orientedat an angle of at least about 45 degrees relative to horizontal whilethe aircraft ascends.

The aircraft can also descend with the envelope in a substantiallyfilled configuration by receiving air in the envelope as the lift gas isvented. The air and lift gas mix during descent to avoid sloshing of thegases and resulting instability. The aircraft can be recovered andlaunched repeatedly.

The present invention also provides an apparatus for launching anaircraft. The apparatus includes first and second masts that areconfigured to be connected to the first and second ends of the envelopeso that the masts support the aircraft therebetween in a substantiallyhorizontal configuration. The second mast is rotatably connected to theenvelope so that the envelope can be rotated to an inclined orientationwhen the first mast is disconnected from the envelope. A gas injectiontube is configured to be inserted into the envelope of the aircraft andto extend from a gas source to an upper portion of the envelope. A liftdevice, such as a buoyant balloon, which can be connected to the firstend of the envelope, is configured to lift the first end of the envelopewhen the first mast is disconnected from the envelope and rotate theenvelope to the inclined orientation. The masts can be rollably movableand can be rotatably connected to the envelope to allow rotation of theenvelope about an axis generally parallel to the longitudinal axis.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is an elevation view illustrating a LTA aircraft supported by alaunch apparatus according to one embodiment of the present invention;

FIG. 2 is an elevation view of the aircraft and launch apparatus of FIG.1 partially filled with a lift gas;

FIG. 3 is an elevation view of the aircraft and launch apparatus of FIG.1 with the aircraft rotated to an inclined orientation;

FIG. 4 is an elevation view of the aircraft and launch apparatus of FIG.1 with the aircraft further rotated to a launch position;

FIG. 5 is a partial perspective view of an aircraft and launch apparatusaccording to another embodiment of the present invention;

FIG. 6 is an elevation view of the aircraft and launch apparatus of FIG.5;

FIG. 7 is an elevation view of the aircraft and launch apparatus of FIG.6 with the aircraft rotated to an inclined orientation;

FIG. 8 is an elevation view of the aircraft and launch apparatus of FIG.6 with the aircraft further rotated to a launch position;

FIG. 9 is an elevation view of an aircraft and launch apparatusaccording to another embodiment of the present invention;

FIG. 10 a partial section view of the aircraft of FIG. 9; and

FIG. 11 is an elevation view of an aircraft according to one embodimentof the present invention in an inclined orientation while ascending.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments of the invention are shown. Indeed, this invention may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will satisfy applicable legalrequirements. Like numbers refer to like elements throughout.

Referring now to the drawings, and in particular to FIG. 1, there isillustrated a lighter-than-air (LTA) aircraft 50 supported by a launchapparatus 10 having first and second masts 12, 14 configured to connectto a bow 52 and stem 54 of the aircraft 50, respectively. The aircraft50 can be used for transportation, observation, communication, and avariety of other purposes. For example, the aircraft 50 can be a highaltitude platform (HAP), which can ascend to an altitude of 50,000 feetor higher and includes communication equipment, such as equipment forwireless telephone or radio communication. The aircraft 50 includes anenvelope 56, or pouch configured to receive and contain a lift gas andthereby provide buoyancy for lifting the aircraft 50. The envelope 56can be formed of a variety of hermetic materials, as is known in theart, such as a fibrous material with a coating or laminated film on oneor both sides thereof. For example, the envelope 56 can be formed ofmaterials such as polyester or Vectran® fabric, a registered trademarkof Hoechst Celanese Corp. The envelope 56 can be coated withpolyurethane or rubber, or the envelope 56 can be laminated with filmsof Mylar® and/or Tedlar® films, registered trademarks of E. I. du Pontde Nemours and Company. The aircraft 50 can be of blimp-typeconstruction, i.e., without a rigid structure. Alternatively, astructure or frame (not shown) formed of aluminum, titanium, metalalloys, composite materials, and the like can be provided inside and/oroutside the envelope 56. The structure can include a gondola 57 foraccommodating people or equipment.

The envelope 56 can be formed of a non-rigid material that is held in adesired shape or configuration by the pressure of the gas within theenvelope 56. For example, a longitudinal axis 58 of the envelope 56 canextend between the bow 52 and stem 54 of the aircraft 50, thelongitudinal axis 58 of the envelope 56 generally corresponding to alongitudinal axis of the aircraft 50. Further, fins 60, wings, rudders,elevators, and other aerodynamic control devices for controlling themotion of the aircraft 50 can be formed of stiff materials or can beinflatable. Thus, the configuration of the aircraft 50 can be achievedby filling the envelope 56 and/or control devices with gas.

The masts 12, 14 of the apparatus 10 can be connected to the envelope 56of the aircraft 10 via connection devices such as cones 16, 18. Thecones 16, 18 are formed of battens 20, which are strips or other piecesof rigid reinforcement material that are connected to the envelope 56and spread the forces associated with the connections to the masts 12,14 over the area of the battens 20. The battens 20 can be tied, sewn,glued, welded, or otherwise fastened to the envelope 56, and one or bothof the cones 16, 18 can be removable from the envelope 56, as furtherdiscussed below. Each cone 16, 18 also includes a connection feature 22such as a ring, hook, or any swiveling connection that is attached tothe battens 20 and provides a point of connection for engaging a hook orother connection portion of the respective mast 12, 14. Thus, the masts12, 14 can be connected and disconnected from the envelope 56, and theaircraft 50 can be supported by the masts 12, 14 such that thelongitudinal axis 58 of the envelope 56 extends substantially horizontalbetween the two masts 12, 14. The connection features 22 of the cones16, 18 can be attached on the axis 58 of the envelope 56 or off-centerfrom the axis 58. For example, as shown in FIG. 1, the first mast 12 isconnected to the first cone 16 at the center of the bow 52 of theaircraft 50, and the second mast 14 is connected to the second cone 18off-center from the axis 58 of the envelope 56.

Each of the masts 12, 14 can be a wheeled device such as a motorizedvehicle of sufficient weight to anchor the aircraft 50. For example,each mast 12, 14 can be a motorized truck weighing several tons. Themasts 12, 14 are sufficiently tall to support the aircraft 50 above theground, as shown in FIG. 1, and the masts 12, 14 can be of fixed heightor adjustable, such as by extending or retracting telescoping sectionsof the masts 12, 14. The masts 12, 14 can also provide rotatableconnections 24 to the aircraft 50 so that the aircraft 50 can be rotatedabout an axis generally parallel with the longitudinal axis 58 as wellas an axis perpendicular to the longitudinal axis 58. Further, one orboth of the masts 12, 14 can have a hinge 26 or other device for hingingor rotating so that the aircraft 50 can be rotated to an inclinedorientation and rotated relative to the respective mast 12, 14. Thehinge 26 can also be rotated to adjust the height of the aircraft 50 andthe position of the aircraft 50 relative to the masts 12, 14, forexample to facilitate the installation of a propeller on the propulsionunit 28. Flexible connection devices such as ropes or chains can be usedas the primary connections between the masts 12, 14 and cones 16, 18 oras secondary connections therebetween.

According to one construction method of the present invention, theaircraft 50 is assembled in a hangar at the launch site. First, theenvelope 56 can be spread out on a work surface, visually inspected, andtested for leaks by filling and pressurizing the envelope 56 with air.Next, certain structural components and other equipment of the aircraft50 can be assembled with the envelope 56, such as an internal frame orload distribution system; electrical wires and conduits therefor; gascontrol devices such as pipes, hoses, and valves used to regulate theflow of gas to and from the envelope 56; a payload, which can be locatedinside or outside the envelope 56; and cables for bracing andcontrolling the fins 60 or other aerodynamic control structures. Thefins 60 can be welded to the envelope 56 and can be inflated orotherwise configured before, during, or after the ascent of the aircraft50. Also, a propulsion unit 28 such as an engine or other thrust devicecan be connected to the envelope 56. The components and equipment can beinstalled while the envelope 56 is partially inflated with air, and thevolume of air in the envelope 56 can be adjusted during assembly tofacilitate access to the different parts of the envelope 56.

The envelope 56 can then be substantially filled with air so that theenvelope 56 is configured to a shape similar to its typical shape duringflight, with the exception of a flattened portion of the envelope 56that is supported by the work surface. The battens 20 of the cones 16,18 are then attached to the respective ends of the envelope 56.Preferably, the battens 20 of the first cone 16 are releasably connectedto the bow 52 so that the first cone 16 can be quickly and easilydisconnected from the aircraft 50. Cranes or other lifting equipment canthen be used to lift the aircraft 50 using the connection features 22 onthe cones 16, 18, and the connection features 22 can then be connectedto the masts 12, 14 as illustrated in FIG. 1. With the aircraft 50suspended between the masts 12, 14, the aircraft 50 can be rotated and alocking mechanism on the masts 12, 14 can be used to restrain theaircraft 50 in various rotational positions to facilitate access to thedifferent portions of the envelope 56 while further assembly isperformed. For example, the aircraft 50 can be rotated so that aparticular portion of the envelope 56 is located at a bottom or sideposition of the aircraft 50, and a person on a crane or other elevatingdevice can access the envelope 56 to install equipment, inspect theenvelope 56, and the like. Equipment installed on the envelope 56, suchas solar cells, can be installed in its final or operating position orconfiguration. The aircraft 50 can be moved while suspended from themasts 12, 14, for example, by rollably moving the masts 12, 14 out ofthe hangar and possibly to a launch area.

As shown in FIG. 2, one or more restraining lines 30 can be connected toreinforced patches 62 on the envelope 56. The restraining lines 30 canbe secured to winches 32 or other line control devices. A gas injectiontube 36 can be connected to a gas source 40 and fluidly connected to theenvelope 56. For example, the gas injection tube 36 can be partiallyinserted into the envelope 56 of the aircraft 50 as illustrated in FIG.2. The gas source 40 is configured to supply the lift gas, such ashelium, and the injection tube 36 is configured to direct the lift gasinto the envelope 56. The gas injection tube 36 can be inserted into theenvelope 56 to a position near the top 55, or upper portion, of theenvelope 56, and a diffuser 38 can be provided on the end of the tube 36inside the envelope 56 to slow the speed of the gas entering theenvelope 56 and reduce the mixing of the gases therein. The tube 36 isformed of a lightweight fabric or other flexible material.Alternatively, the tube 36 can be positioned outside the envelope 56 andconnected to a port located at the desired point of entry of the liftgas, for example, at the upper portion 55 of the envelope 56.

According to one embodiment of the present invention shown in FIG. 2,the envelope 56 is inflated with air and supported by the apparatus 10.The gas injection tube 36 is then inserted through a port in theenvelope 56 and the lift gas is injected into the envelope 56 near thetop 55 of the envelope 56 so that the lift gas enters and pools at thetop 55 of the envelope 56 and air is vented through one or more valvesat the bottom of the envelope 56. Preferably, as the helium replaces theair in the envelope 56, the helium and the air remain substantiallyseparate in pools 64, 66 of the respective gases. A mixed gas, i.e., amixture of the helium and the air, forms in a boundary layer 68 betweenthe helium pool 64 and the air pool 66 in the envelope 56. The boundarylayer 68, i.e., the mixed gas, moves downward as additional helium isinjected into the envelope 56. As the amount of helium in the envelope56 increases, the buoyancy of the envelope 56 increases, and the weightof the aircraft 50 that is supported by the masts 12, 14 decreases.

When the envelope 56 contains a sufficient amount of helium to lift theaircraft 50, the restraining line 30 is tightened and the cone 16 on thebow 52 of the envelope 56 is removed, disconnecting the aircraft 50 fromthe first mast 12. Then, as shown in FIG. 3, the restraining line 30 isextended so that the bow 52 of the aircraft 50 rises and the aircraft 50rotates relative to the second mast 14, the longitudinal axis 58 of theaircraft 50 becoming inclined. Preferably, the restraining line 30 isextended smoothly and gradually by the winch 32 or other line controldevice so that the motion of the aircraft 50 is controllably adjustedand the mixing of the gases in the envelope 56 is minimized. When theaircraft 50 is rotated to a launch configuration, shown in FIG. 4, therestraining line 30 can be released, and the second mast 14 can bereleased from the second cone 18 to launch the aircraft 50, which thenbegins to ascend. In one embodiment, the launch position is a positionin which the center of volume of the lifting gas 70 of the aircraft 50is located directly above the center of gravity 72 of the aircraft 50.The center of volume of the lifting gas 70 is the gravitational centerof the lift gas within the envelope 56.

While the lift provided by the helium in the envelope 56 rotates theaircraft 50 to the launch position in the foregoing example, a liftdevice can alternatively be used as illustrated in FIGS. 5–8. The liftdevice can be a buoyant vessel such as balloon 42, as shown in FIG. 5,which is filled with hydrogen, helium, or another gas that is lighterthan air. The balloon 42 is restrained by one or more balloon controllines 44, which extend from the balloon 42 and are connected to winches46 or other line control devices. Connection lines 48 that extend fromthe balloon 42 are configured to be connected to the aircraft 50. Thus,the aircraft 50 can be supported by the masts 12, 14 and moved by themasts 12, 14 to the balloon 42. The connection lines 48 are connected toreinforced patches 62 on the envelope 56, as shown in FIG. 6, and thecontrol lines 44 can be loosened so that the balloon 42 exerts an upwardforce on the envelope 56, thereby taking some or all of the weight ofthe aircraft 50 off of the first mast 12. The first mast 12 is thendisconnected from the envelope 56 by releasing the cone 16 or thebattens 20 so that the cone 16 is released from the envelope 56 or themast 12. The balloon 42 is sufficiently buoyant to lift the bow 52 ofthe aircraft 50 and rotate the envelope 56 about the second mast 14 atleast partially toward the launch position as the control lines 44 areextended, as shown in FIG. 7. For example, if the envelope 56 has amaximum take-off weight (MTOW) of about 20 tons, the balloon 42 couldhave a lift capacity of about 12 tons. For example, a spherical balloon42 with a diameter of about 30 meters and filled with hydrogen can beused.

The gas injection tube 36 is inserted into the envelope 56, and heliumor another lift gas is injected into the top portion 55 of the envelope56 as described above. As shown in FIG. 8, the tube 36 can be insertedthrough a port in the stern 54 of the envelope 56 and extended to thebow 52 of the aircraft 50. Thus, the helium enters the top 55 of theenvelope 56, i.e., the highest portion of the envelope 56, and air isvented through valves at a lower portion of the envelope 56, i.e., nearthe stern 54 of the aircraft 50. When sufficient helium has beeninjected to lift the aircraft 50, the balloon 42 can be released fromthe aircraft 50, for example, using a remote-controlled electronic orpyrotechnic actuator 74 that disconnects the connection lines 48 fromthe aircraft 50. The second mast 14 is also disconnected from theaircraft 50, launching the aircraft 50 to begin its ascent. The tube 36can be removed from the envelope 56 or can remain therein during flight.A remote controlled valve on the balloon 42 can be actuated to vent thegas from the balloon 42, and/or the control lines 44 can be used to pullthe balloon 42 back towards the ground.

According to another embodiment of the present invention, a gas bag 80can be provided in the envelope 56 and configured to receive the liftgas from the gas source 40 to keep the lift gas from mixing with thesecond gas in the envelope 56 until a desired time. For example, asshown in FIGS. 9 and 10, the gas bag 80 is connected to a cover 82 thatis used to close an orifice 83 in the envelope 56. The orifice 83 islocated at one end of the envelope 56, and the envelope 56 is reinforcedby a reinforcement ring 84 that extends circumferentially around theorifice 83. The cover 82 is connected to the reinforcement ring 84during assembly such that the cover 82 seals the orifice 83. The cover82 can include an injection port 86 for receiving the lift gastherethrough, i.e., from the source 40 and into the gas bag 80. Further,a ripcord 88 or other control device can extend through a sealed port 89in the cover 82 so that the gas bag 80 can be opened from outside theenvelope 56.

Thus, the gas bag 80, which can be formed of a lightweight plastic filmand sealed to the cover 82, can be inserted into the envelope 56 throughthe orifice 83 during assembly of the aircraft 50. The cover 82 is thenconnected to the reinforcement ring 84. The gas source 40 is connectedto the port 86 and the lift gas is delivered to the gas bag 80, whichcan be of sufficient size to hold all of the lift gas required foroperation of the aircraft 50. A net 90 or other bulkhead can be providedin the envelope 56 can support the gas bag 80 and restrict expansionand/or movement of the gas bag 80 within the envelope 56.

The gas bag 80 can be filled with the lift gas at any time during theassembly or launch of the aircraft 50. For example, the gas bag 80 canbe filled while the aircraft 50 is still in a hangar so that the liftgas provides buoyancy to the aircraft 50 while the aircraft 50 is movedout of the hangar. The aircraft 50 can be supported by the masts 12, 14,as described above, while the aircraft 50 is moved to the desiredlaunching site. The masts 12, 14 can be attached to the connectionfeatures 22 of the envelope 56, which can be located at the bow 52 andstem 54 or other positions on the envelope 56.

Launch is accomplished by releasing the aircraft 50 from the first mast12 so that the aircraft 50 rotates to a vertical position, similar tothat illustrated in FIG. 8. Restraining lines 30 can also be used tocontrol the rotation of the aircraft 50, as described above. The ripcord88 is used to open the gas bag 80 so that the lift gas in the gas bag 80is released therefrom in the envelope 56. For example, the ripcord 88can be pulled to tear the gas bag 80 or actuate a device for opening thebag 80. The lift gas then begins to mix with the second gas in theenvelope 56 to form the boundary layer 68, as described in connectionwith FIG. 8. Upon release of the aircraft 50 from the second mast 14,the aircraft 50 begins to ascend. After flight, the gas bag 80 and thecover 82 can be removed from the aircraft 50 and replaced with a new gasbag and cover for a subsequent flight.

FIG. 11 illustrates an aircraft 50 launched by any of the methodsdescribed above in connection with FIGS. 2–4, 5–8, and 9–10. In theinclined configuration during ascent, the helium pool 64 is located atthe upper end 55, i.e., bow 52, of the envelope 56, and the air pool 66is located at the lower, i.e., stem 54, of the envelope 56. The boundarylayer 68 formed of the mixed gas is between the helium and air pools 64,66. As the aircraft 50 ascends and the atmosphere becomes decreasinglydense, the helium and the air expand. Air from the lower portion of theenvelope 56 is vented to the atmosphere, and the boundary 68 formed bythe mixed gas moves lower in the envelope 56. Nearly all of the air canbe vented from the envelope 56 so that the aircraft 50 contains littleor no air when it reaches a desired flight altitude. The time requiredfor ascent depends on the rate of ascent and the desired flightaltitude. For example, an ascent time of about 1 hour, 11 minutes wouldbe required for the aircraft 50 to climb to a flight altitude of 70,000at a rate of about 5 meters per second (16.4 feet per second). At anascent rate of 1 meter per second (3.3 feet per second), the same ascentwould take about 5 hours, 54 minutes. The rate of ascent can becontrolled by venting lift gas from the envelope 56 and/or by droppingballast from the aircraft 50. Ballast can be carried at the stem 54 ofthe aircraft 50 to balance the aircraft 50 in the upright orientationillustrated in FIG. 11.

The mixed gas that forms the boundary layer 68 can also be vented fromthe envelope 56. As the mixed gas is vented, the buoyancy of theaircraft 50 is reduced, thereby slowing the ascent of the aircraft 50.Additionally, as indicated in FIG. 11, the center of volume of thelifting gas 70 of the aircraft 50 moves toward the stem 52 as the air isvented therefrom and the gas within the envelope 56 becomessubstantially homogenous throughout. Ballast can also be adjusted orjettisoned to adjust the weight balance or net buoyancy of the aircraft50. For example, water, other liquids, or sand can be held in ballastbags (not shown) on the aircraft 50 and redistributed on the aircraft 50or released. Thus, as the aircraft 50 approaches and reaches the desiredflight altitude, the orientation of the aircraft 50 can be adjusted sothat the longitudinal axis 58 is adjusted from the inclined orientationto a horizontal or nearly horizontal flight orientation.

During flight, the propulsion unit 28, fins 60, and other maneuveringequipment can be used to control the speed, direction, and orientationof the aircraft 50 as is known in the art. The aircraft 50 can alsoinclude one or more ballonets that are full of air upon takeoff and usedduring flight to regulate the gas pressure in the envelope 56. Thepropulsion unit 28, fins 60, and other maneuvering equipment can be usedto adjust the altitude of the aircraft 50 and/or descend for landing.Helium can also be vented from the envelope 56 during descent, and aircan be received into the envelope 56 such that the volume of theenvelope remains substantially constant. Blowers or fans in the envelope56 can be used to pump the air into the envelop 56 and to mix the gastherein to prevent separation of the helium and air, thus avoidinginstability due to pooling and/or sloshing of the gases. The aircraft 50can be landed onto the ground and then secured again to the masts 12, 14for subsequent launching. Thus, the aircraft 50 can be used for repeatedflights.

Many modifications and other embodiments of the invention set forthherein will come to mind to one skilled in the art to which thisinvention pertains having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the invention is not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

1. A method for launching an aircraft having an envelope for receiving alift gas that is lighter than air, the method comprising: providing theaircraft with a second gas in the envelope, the second gas being heavierthan the lift gas; introducing the lift gas into the envelope of theaircraft so that the aircraft is buoyant and the envelope issubstantially full of a combination of the lift gas and the second gas,the lift gas and the second gas being substantially separate in theenvelope with a mixed gas formed by the lift and second gasestherebetween; releasing the aircraft so that the aircraft ascends; andventing the second gas from the envelope.
 2. A method according to claim1 wherein said providing step comprises providing air as the second gasin the envelope.
 3. A method according to claim 1 wherein saidintroducing step comprises introducing helium into the envelope as thelift gas.
 4. A method according to claim 1 wherein said introducing andreleasing steps comprise releasing the aircraft with a center ofbuoyancy being between the center of gravity of the aircraft and a firstlongitudinal end of the aircraft such that the first end of the aircraftis oriented above a second distal end of the aircraft while the aircraftascends.
 5. A method according to claim 4 wherein said introducing andreleasing steps comprise releasing the aircraft such that an axis of theenvelope extending between first and second ends thereof is oriented atan angle of at least about 45 degrees relative to horizontal while theaircraft ascends.
 6. A method according to claim 1 further comprising:providing at least one mast for supporting the aircraft; securing theaircraft to the at least one mast; and raising a first end of theaircraft to an elevation higher than a second distal end of the aircraftsuch that a longitudinal axis of the aircraft extending between thefirst and second ends is inclined at an angle relative to horizontal. 7.A method according to claim 6 wherein said raising step comprisesconnecting a buoyant balloon to the first end of the aircraft such thatthe balloon lifts the first end of the aircraft.
 8. A method accordingto claim 6 wherein said raising step comprises at least partiallyfilling a gas bag in the envelope with the lift gas such that the gasbag lifts the first end of the aircraft.
 9. A method according to claim6 wherein said securing step comprises securing the first and secondends of the aircraft to first and second masts such that thelongitudinal axis of the aircraft is substantially horizontal.
 10. Amethod according to claim 6 wherein said raising step comprises at leastpartially filling the envelope with the lift gas and releasing the firstend of the aircraft such that the lift gas raises the first end of theaircraft.
 11. A method according to claim 6 further comprising rollablymoving at least one of the masts after said securing step.
 12. A methodaccording to claim 1 wherein said introducing step comprises injectingthe lift gas through a tubular channel extending into the envelope andproximate an upper portion of the envelope to minimize mixing of thelift gas in the envelope.
 13. A method according to claim 1 furthercomprising al least partially venting the lift gas from the envelope andreceiving air in the envelope such that the aircraft descends with theenvelope in a substantially filled configuration.
 14. A method accordingto claim 13 further comprising repeating said introducing, releasing,and first and second venting steps in order to repeat the launching ofthe aircraft.